1. Field of the invention
This invention concerns a method for managing the throughput of digitally coded messages transported through an asynchronous network, particularly an ATM (Asynchronous Transfer Mode) network and a device for its embodiment.
2. Description of the Prior Art
The routing of speech, music, pictures, text and data in general have given rise to multiservice transmission systems.
Telecommunication systems are calling more and more upon a known asynchronous transmission technique, ATM, that accepts digital information with varied and irregular natures and throughputs.
Data streams output from different services are cut into fixed length segments. A header is associated with each segment, also called a data field and is used for routing data from a sending subscriber to a destination subscriber. The total forms a fixed length ATM cell that can be interpreted by what is called an ATM exchange, as a function of the contents of its header.
Transmission lines consisting of cables, radio links, optical fibers, etc., connect exchanges together to form a telecommunications network.
Each exchange is provided with routing information to switch incident ATM cells towards one of the adjacent exchanges.
Thus a virtual circuit can be made within the network corresponding to a routing determined by the cell header between a transmission terminal, or source, and a reception terminal, making use of a physical support materialized by transmission lines. A transmission line may be common to several virtual circuits. The ATM exchange therefore needs to multiplex cells output from different services on the same transmission line.
This multiplexing makes it necessary to estimate the useful throughput of the line, that may be very different depending on which service is considered, to ensure that the physical throughput limited by the transmission medium is sufficient.
However this time averaged estimate does not take account of the irregularity of the ATM transmission. For example a service put on hold for a given time may send a burst of cells all at once. This throughput peak can exceed the capacity of the line, which is harmful for the integrity of data from all services multiplexer on the line.